Rotating scanning antenna apparatus and method for locating buried objects

ABSTRACT

A ground penetrating antenna apparatus and method are provided for locating underground objects via radar, sonar, or similar methods. The apparatus includes one or more antennas that are rotatably affixed to support extensions that also rotate, but about an axis that is different from each of the antenna axes. The apparatus includes a linear propulsion mechanism, and the support extensions may be coupled to the linear propulsion mechanism via a transmission mechanism. In one embodiment, the supporting extensions rotate at a constant rate and each antenna rotates at that same constant rate but in the opposite direction.

FIELD OF THE INVENTION

This invention relates to a rotating, linearly propelled scanningantenna apparatus and method using radar, sonar, or the like, for use inlocating buried objects.

BACKGROUND

In many applications it is important to be able to quickly andaccurately locate objects such as pipes, cables, mines, and barrels thatare buried beneath the surface of the earth. Such objects may be locatedusing Ground Penetrating Radar (“GPR”) techniques in whichelectromagnetic waves are transmitted into the ground and reflected.(The term ‘ground’ includes soil, concrete, asphalt, and the like.) Thereflections are analyzed according to methods that are well known in theart to determine the location of any object that may be buried therebeneath. Other methods well known in the art may also be used, includingsonar techniques and inductive techniques.

GPR techniques use transmitting antennas to emit the electromagneticwaves that propagate into the ground and interact with the buriedobjects. This interaction results in a scattered wave, which is measuredby the receiving antenna of the GPR device. By changing the location ofthe transmitting antenna and recording the corresponding signal that isreceived and then output by the receiving antenna as a function of time(or frequency) and location, one obtains the radar data from which theinformation about the buried objects may be extracted. However, for theradar data to be useful, the positions of the measurement locations mustbe accurately known. Further, it is important for cost efficiency thatthe system be able to cover a large area in a short period of time; thatis, it is important that the system have a high survey speed, whichmeans that the antenna must travel at a high speed.

Such high speed movement may create undesirable mechanical stresses onthe antennas. For example, in the simplest scanning system the antennamoves linearly back and forth across the width of the scanning area.This back and forth linear motion requires that the antenna slow down,stop, and then speed up each time it reaches the edge of the scanningarea. This type of back and forth movement creates tremendous mechanicalstresses in the antennas and survey system when the system is operatedat a high survey speed. In fact, these extreme stresses severely limitthe survey speed that is obtainable with a linear scanning system.

It is an object of the current invention to provide a rotating GPRsystem for which the antenna speed and survey speed can be very highwithout causing excessive mechanical stresses on the antennas andscanning system. With a rotating system, the antennas do not have toslow down when they reach the edge of the scanning area, but instead mayoperate at a constant speed. As a consequence, the mechanical stressesare much less for a rotating GPR system than for a linear GPR system.

A rotating GPR system is described in U.S. Pat. No. 4,967,199 (“GroundProbing Radar Method and Apparatus”) to Gunton et al. and in SurfacePenetrating Radar by D. J. Daniels (IEE Press, 1996, pp. 200-204). Thosereferences describe a system in which the antennas are interleavedspirals whose axes correspond with the axis of rotation. Further, unlikethe present invention, the rotation in these systems is used solely toreduce clutter rather than to move the antenna system along the ground.

SUMMARY OF THE INVENTION

According to the objects of the present invention, a ground penetratingantenna apparatus is described providing an antenna housing, one or moresupporting extensions that are rotatably affixed to the antenna housingabout a first axis, at least one antenna that has transmit and receiveelements and that is rotatably affixed to a supporting extension about asecond axis that is different from the first axis, a linear propulsionmechanism that is attached to the housing so that the housing may bemoved over the ground, an impulse generator that is electrically coupledto each transmit element so as to provide pulses to each transmitelement, and a sampling unit that is electrically coupled to eachreceive element so as to receive the output from each receive element.

In one embodiment of the present invention, the ground penetratingantenna apparatus comprises radar antennas. In a father embodiment, asupporting extension is responsive to the linear propulsion mechanism.In yet another embodiment, a supporting extension is coupled to thelinear propulsion mechanism via a transmission mechanism.

In one embodiment of the present invention, each supporting extensionrotates at a constant rate of rotation. In another embodiment, eachsupporting extension rotates at a constant rate and the antenna rotatesat a constant rate of rotation that is equal in magnitude and oppositein direction to the constant rate of rotation of each supportingextension.

In one embodiment of the present invention, the linear propulsionmechanism comprises a cart that is coupled to the housing and a meansfor propelling the cart. In another embodiment, the linear propulsionmechanism comprises a self-propelled vehicle that is coupled to thehousing.

In one embodiment of the present invention, the ground penetratingantenna apparatus further comprises a data storage device for storingthe radar data collected from the sampling unit. In another embodiment,the apparatus further comprises a position indicator that is coupled tothe supporting extension and the linear propulsion mechanism. In yetanother embodiment, the apparatus further comprises a data storagedevice for storing the radar data collected from the sampling unit andthe position data collected from the position indicator. In anotherembodiment, each element of the radar data corresponds to a uniqueelement of the position data.

Also in accordance with the objects of the present invention, a methodis provided for locating underground objects within a surface areaconsisting of providing a housing that is adapted for linear movement,providing a supporting extension that is rotationally coupled to thehousing about an axis, providing an antenna that is rotationally coupledto a supporting extension about an axis different from said axis of saidsupporting extension, providing electronics coupled to the antenna thatis capable of receiving ground penetrating antenna data, rotating asupporting extension about the axis of the supporting extension,rotating the antenna about the axis of the antenna, moving the housingalong a path within the surface area, receiving ground penetratingantenna data at selected positions along the path, recording the groundpenetrating antenna data and the selected positions, and analyzing therecorded antenna data and the recorded selected positions to locateunderground objects. In one embodiment, the antenna is a radar antenna.

In one embodiment of the present invention, the step of rotating asupporting extension further comprises rotating a supporting extensionat a constant rate of rotation. In another embodiment, the rotating stepcomprises rotating an antenna at a constant rate that is equal inmagnitude and opposite in direction to the constant rate of rotation ofa supporting extension.

In one embodiment of the present invention, the step of moving thehousing further comprises moving the housing responsively to rotating asupporting extension. In another embodiment, the step of moving thehousing further comprises providing a cart that is coupled to thehousing and propelling the cart. In yet another embodiment, the step ofmoving the housing further comprises providing a self-propelled cartthat is couples to the housing. In another embodiment, the recordedantenna data is converted from polar coordinates to rectangularcoordinates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a four antenna apparatus in accordance with thepresent invention having two arms (i.e., four supporting extensions).

FIG. 2 is a top view of a three antenna apparatus in accordance with thepresent invention having two arms (i.e., four supporting extensions).

FIG. 3 is a top view of a three antenna apparatus in accordance with thepresent invention having three spokes (i.e., three supportingextensions).

FIG. 4 is a side view of an apparatus in accordance with the presentinvention with two antennas.

FIG. 5 is a [top] side view of an apparatus in accordance with thepresent invention with one antenna.

FIG. 6 is a [side] top view of an apparatus in accordance with thepresent invention with one antenna.

DETAILED DESCRIPTION

One embodiment of the present invention uses a radar system thatincludes a radar antenna attached to the end of a rotating arm whoseaxis of rotation is perpendicular to the ground. The system moves alongthe ground in a linear path while the rotating arm (and the attachedantenna) turn about their axes of rotation. With the present system, theradar antennas rotate about axes that are independent of the centralaxis of rotation. In this way, the present system permits a largercoverage area than is provided by a single axis system. Further, with amultiple axis system, it is possible for the antennas to maintain afixed orientation regardless of the position of the arm to which theyare attached. For example, in a system with two antennas, each antennamay rotate about its own axis at the same rotational speed as the armbut in an opposite direction, thereby maintaining a constant orientationwith respect to the linear movement of the system. Typically the forwardlinear motion of the system will be much slower than the rotating motionof the antenna, so that after one revolution of the antenna, itsposition will have changed by only a small fraction of the radius of therotating arm. In a second embodiment, an antenna may be attached to eachend of the rotating arm. The width of the survey area is equal to twicethe radius of the rotating arm.

Although the embodiment described below includes a single rotating armwith either an antenna at one end or an antenna at both ends, thepresent invention is not limited to those configurations. Instead, thesystem could contain multiple arms. For example, referring to FIG. 1, afour-antenna system could contain two arms (i.e., four extensions 120,120′, 120″, 120′″) with an antenna 110 at the end of each extension 120.Alternately, as shown in FIG. 2, a three-antenna system could containtwo arms (i.e., four extensions 120, 120′, 120″, 120′″) with an antenna110 at the end of three extensions 120, 120′, and 120″, but no antennaat the end of the fourth extension 120′″. Instead of arms, the systemcould use spokes. For example, referring to FIG. 3, a three-antennasystem could contain three spokes (i.e., three extensions 130, 130′,130″), with an antenna 110 at the end of each extension. In this way,any number (odd or even) of antennas can be accommodated using either anarm or a spoke configuration. In this description, the term “supportingextension” will include both arm extensions and spoke extensions. Forexample, a system with two arms would have four supporting extensions,whereas as a system with three spikes would have three supportingextensions.

FIG. 4 and FIG. 5 show a side view and a top view, respectively, of asystem with an antenna array consisting of a single antenna 110. Housing140 is shown with wheels 150 on ground 160. Also shown are the directionof linear motion 170, the axis of rotation 190 for the antenna array,the axis of rotation 200 for the single antenna 110, the direction ofrotating motion 180 about axis 190 for the antenna array, and thedirection of rotation 210 for antenna 110 about axis 200.

In one embodiment, the rotating motion is provided by a directconnection to the linear driving mechanism via, for example, a gearmechanism lining the axle of the center arm to an axle of a wheel on atransporting vehicle. With this embodiment, the system moves forward afixed distance for each 360° of rotational movement. However, it is notnecessary for the rotating mechanism to be directly connected to thelinear driving mechanism provided that the angular position of theantennas and the position of the axis of rotation are shown at each datacollection point. There are two advantages to providing a system inwhich the rotational mechanism is not linked to the linear drivingmechanism. First, with separate systems the rotational speed can remainconstant even when the linear speed varies due, for example, toobstacles or hills in the survey area. (Maintaining a constant linearspeed under such conditions is difficult.) Second, the motor thatprovides the rotational motion can be relatively small since only asmall amount of work is required to maintain a constant rotationalspeed.

One such GPR system with an antenna at each end of the rotating arm isshown in FIG. 6. In particular, a separate antenna is attached to eachof the two support plates 11. Each antenna is contained within aseparate antenna enclosure 12. The rotating parts of the system areenclosed within housing 13. The support plates 11 are attached throughthrust bearings 15 to a support collar 10, which in this embodiment isthe rotating arm itself. Each thrust bearing 15 is supported by a collar8. The power and data cables for each antenna pass through rotationalelectrical connectors 7, connect to cable 6, and exit housing 13 throughthe main rotational electrical connector 2. The axis of rotation of thesupport carrier 10 is the center of rotational hub 1, which is attachedto bearing 14. The rotating motion is sustained by drive assembly 3,which includes an electric motor. The support plates 11 preferablycounter-rotate so that the antenna orientation remains constant. Thiscounter-rotation may be achieved by stationary gear 4 that is attachedin FIG. 6 directly to support carrier 10, walling gear 5, and drive gear9.

The linear motion of the system can be provided by a number of differentdrive systems, all well known in the art. For example, the entire systemcould be mounted on a cart that is pulled by a vehicle or a winch.Alternately, the system could be mounted directly onto a self-propelledvehicle or the linear motion could be linked directly to the rotationaldrive mechanism.

The angular position of the arm may be determined by using an encoderthat measures the angle between the central arm and some fixeddirection. Such encoders are well known in the art and may be obtained,for example, from Litton Poly-Scientific of Blacksburg, Virginia.

The position of the system along its linear path can be determined usinga number of techniques that are well known in the art. For example, asurvey wheel could be attached to the vehicle that moves the systemalong the ground. Such a survey wheel could provide a measurement of thedistance traveled by the vehicle. This information could then becombined with the information from the encoder to provide a record ofantenna position corresponding to each radar data collection point. Theradar data and the positional data could be continuously merged into asingle file for subsequent processing. If the linear motion and therotational motion remain constant throughout the data collection, thenit is not necessary to continuously merge the radar and position data.

Systems for providing the actual radar electronics and methods foranalyzing radar data to determine object locations are well known in theart and any such system and method may be used with the presentinvention. The radar electronics and the mechanical transport androtational system are connected through various encoders that indicatewhen the radar system should take a data reading. For example, the radarsystem could be set to take one measurement for every 10° of rotation ofthe central arm or for every 1 inch of travel in the forward direction.

With regard to the analysis of the data collected, it should be notedthat many analysis routines assume that the input data is provided in arectangular grid. Although data collected in accordance with thedisclosed embodiments will not be in a rectangular grid, it may beconverted to a rectangular grid via standard interpolation techniquesthat are well known to those of skill in the art.

Finally, although this invention has been described via an embodimentbased on radar antennas, it is not intended that the present inventionbe limited to radar signals. One of skill in the art would know ofnumerous other sensors that could be used to practice the presentinvention. Further, one of skill in the art would understand how thedescribed embodiment could be modified to accommodate other sensors. Forexample, the present invention could be used with inductive sensors orsonar sensors. Further, various types of sensors could be combined inthe same system.

The present invention, therefore, is well adapted to carry out theobjects and obtain the ends and advantages mentioned above, as well asothers inherent herein. All presently preferred embodiments of theinvention have been given for the purposes of disclosure. Where in theforegoing description reference has been made to elements having knownequivalents, then such equivalents are included as if they wereindividually set forth. Although the invention has been described by wayof example and with reference to particular embodiments, it is notintended that this invention be limited to those particular examples andembodiments. It is to be understood that numerous modifications and/orimprovements in detail of construction may be made that will readilysuggest themselves to those skilled in the art and that are encompassedwithin the spirit of the invention and the scope of the appended claims.

We claim:
 1. A ground penetrating antenna apparatus, comprising: anantenna housing; at least one supporting extension wherein each saidsupporting extension is rotatably affixed to said antenna housing abouta first axis; at least one antenna, comprising transmit and receiveelements, that is rotatably affixed to one of said at least onesupporting extension about a second axis different from said first axis;a linear propulsion mechanism attached to said housing whereby saidhousing may be moved over the ground; an impulse generator electricallycoupled to each of said one or more transmit elements so as to providepulses to each said transmit element; and, a sampling unit electricallycoupled to each of said one or more receive elements so as to receivethe output from each said receive element.
 2. The ground penetratingantenna apparatus of claim 1 wherein each said antenna is a radarantenna.
 3. The ground penetrating antenna apparatus of claim 2 whereineach said supporting extension is responsive to said linear propulsionmechanism.
 4. The ground penetrating antenna apparatus of claim 3wherein at least one said supporting extension is coupled to said linearpropulsion mechanism via a transmission mechanism.
 5. The groundpenetrating antenna apparatus of claim 2 wherein each said supportingextension rotates at a constant rate of rotation.
 6. The groundpenetrating antenna apparatus of claim 5 wherein each said antennarotates at a constant rate of rotation that is equal in magnitude andopposite in direction to said constant rate of rotation of each saidsupporting extension.
 7. The ground penetrating antenna apparatus ofclaim 2 wherein said linear propulsion mechanism comprises a cartcoupled to said housing and a means for propelling said cart.
 8. Theground penetrating antenna apparatus of claim 2 wherein said linearpropulsion mechanism comprises a self-propelled vehicle coupled to saidhousing.
 9. The ground penetrating antenna apparatus of claim 2 furthercomprising a data storage device for storing radar data collected fromsaid sampling unit.
 10. The ground penetrating antenna apparatus ofclaim 2 further comprising a position indicator coupled to at least onesaid supporting extension and said linear propulsion mechanism.
 11. Theground penetrating antenna apparatus of claim 10 farther comprising adata storage device for storing radar data collected from said samplingunit and position data collected from said position indicator.
 12. Theground penetrating radar apparatus of claim 11 wherein each element ofsaid radar data corresponds to a unique element of said position data.13. A method of locating underground objects within a surface areacomprising: providing a housing adapted for linear movement; providing asupporting extension rotationally coupled to said housing about an axis;providing an antenna rotationally coupled to said supporting extensionabout an axis different from said axis of said supporting extension;providing electronics coupled to said antenna capable of receivingground penetrating antenna data; rotating said supporting extensionabout said axis of said supporting extension; rotating said antennaabout said axis of said antenna; moving said housing along a path withinsaid surface area; receiving ground penetrating antenna data at selectedpositions along said path; recording said ground penetrating antennadata and said selected positions; analyzing said recorded antenna dataand said recorded selected positions to locate said underground objects.14. The method of claim 13 wherein said antenna is a radar antenna. 15.The method of claim 14 wherein said rotating said supporting extensionstep a further comprises rotating said supporting extension at aconstant rate of rotation.
 16. The method of claim 15 wherein saidrotating said antenna further comprises rotating said antenna at aconstant rate that is equal in magnitude and opposite in direction tosaid constant rate of rotation of said supporting extension.
 17. Themethod of claim 14 wherein said moving said housing step farthercomprises moving said housing responsively to rotating said supportingextension.
 18. The method of claim 14 wherein said moving said housingstep further comprises: providing a cart coupled to said housing; and,propelling said cart.
 19. The method of claim 14 wherein said movingsaid housing step further comprises providing a self-propelled cartcouples to said housing.
 20. The method of claim 14 further comprisingthe step of converting said recorded antenna data from polar coordinatesto rectangular coordinates.